JPH09215188A - Dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the power conversion efficiency by providing means for determining the on/off timing of a switching element based on a signal from means for detecting the end of regeneration of exciting energy from a transformer to an input power supply, and an output from an error amplifier. SOLUTION: First winding 26a of a transformer 26 and an input power supply 1 are connected with a main switch element, i.e., a field effect transistor 27. When the output D from a triangular wave generation circuit 32 exceeds the output C from an error amplifier 31 at time T1 , the main switch element 27 is turned off and exciting energy stored in the transformer, when the main switch element 27 is turned on, is regenerated from the third winding 26C to the input power supply 1. When regeneration of exciting energy ends at time T2 , the main switch element 27 is turned on and the operation is repeated. According to the arrangement, exciting energy can be regenerated from to the input power supply 1 and a DC/DC converter having high power conversion efficiency can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching frequency variable type DC / DC converter.

[0002]

2. Description of the Related Art FIG. 17 is a circuit diagram showing a conventional DC / DC converter shown in Japanese Patent Publication No. 59-6146. In the figure, 1 is an input power source, 2 is a transistor, 3
Is a transformer, 4 is a resistor, 5 is a capacitor, 6 is a resistor, 7
Is a transistor, 8 is a resistor, 9 is a capacitor, 10 and 1
1 is a diode, 12 is a smoothing reactor, 13 is a capacitor, 14 is a load, 15 is a diode, 16 is a transistor, 17 is an error amplifier, and 18 is a reference power supply.

FIG. 18 is an operation waveform diagram of the DC / DC converter of FIG. 17, and FIG.
18- (b) is the base-emitter voltage of the transistor 7, FIG. 18- (c) is the collector-emitter voltage of the transistor 2, and FIG. 18- (d) is the fourth winding n _4. Is the current that flows through.

Next, the operation will be described. FIG. 18 (a)
When the base current is supplied to the transistor 2 from the resistor 4 connected between the input power source 1 and the base of the transistor 2 at time t ₁ and the collector current flows in the transistor 2, the first winding of the transformer 3 A voltage that further increases the base current of the transistor 2 is generated in the third winding n ₃ via n ₁ , and the transistor 2 immediately shifts to the saturated state by the positive feedback operation. The voltage induced in the _third winding n ₃ is integrated by the resistor 8 and the capacitor 9 as shown in the waveform of FIG. 18B, and when the base-emitter voltage of the transistor 7 reaches the voltage V _BE2 that turns on the transistor. ,
Transistor 7 to the time t ₂ is turned on, in order to short-circuit the base of the transistor 2, transistor 2 is turned off. During the off period of the transistor 2, a counter electromotive voltage is generated in the fourth winding n ₄ in the direction of turning on the diode 15, and the collector of the transistor 16 that is a variable impedance element
Due to the impedance between the emitters, the excitation reset current of the transformer 3 flows as shown in the waveform of FIG. During this period, the collector-emitter voltage of the transistor 2 becomes a value higher than the terminal voltage V _IN of the input power supply 1 as shown in the waveform of FIG. 18C, and the transistor 2 is turned off in the third winding n _3. The voltage that causes
As the base-emitter voltage of, a voltage having the opposite polarity to that when the transistor 2 is turned on as shown in the waveform of FIG. When the exciting current of the transformer 3 finishes discharging through the fourth winding n ₄ at time t ₃ , the base-emitter voltage of the transistor 2 returns to 0, and the operation of turning on the transistor 2 again through the resistor 4 is repeated immediately.

By rectifying and smoothing the voltage generated in the _second winding n ₂ when the transistor 2 is turned on, an output voltage is obtained across the capacitor 13 and supplied to the load 14. When the output voltage obtained across the capacitor 13 rises above the voltage of the reference power supply 18, the output of the error amplifier 17 rises, supplying more base current to the transistor 16. In this state, the collector-emitter impedance of the transistor 16 decreases, and the period from time t _{2 to} t ₃ in FIG. 18 increases. Therefore, the off period of the transistor 2 which is the main switching element increases, and the ratio of the on time to the switching period of the transistor 2, that is, the duty ratio decreases, so that the output decreases. When the output voltage becomes lower than the voltage of the reference power supply 18, the operation reverse to the above operation is performed, and the constant output voltage is supplied to the load 14.

In addition to the above, there is a DC / DC converter using a field effect transistor as a rectifier, which not only can reduce power loss, but also can change the ON / OFF timing of the main switch element. It can also be used as an impedance element.

[0007]

Since the conventional DC / DC converter is configured as described above, the exciting energy of the transformer 3 is consumed by the transistor 16 which is a variable impedance element, and the transformer reset period is consumed. That is, since the non-conduction period of the main switch element 2 is controlled, there is a problem that the power conversion efficiency is deteriorated.

The present invention has been made in order to solve the above-mentioned problems, and a DC / DC converter having high power conversion efficiency
The purpose is to obtain a DC converter.

[0009]

A DC / DC converter according to the present invention is a series circuit composed of a first winding of a transformer, a main switch element and an input power source, the first winding and the above. A series circuit, which is connected in parallel to the main switching element and is configured by the third winding of the transformer and a diode so as to regenerate the excitation energy of the transformer to the input power source, and the second winding of the transformer. A DC / DC converter comprising a rectifying diode and a freewheeling diode connected to each other, the error amplifier amplifying a difference between an output voltage of the converting circuit and a voltage of a reference power source, and an input power source for exciting energy of the transformer. End detection means for detecting the end of regeneration to the ON / OFF timing of the main switch element by the signal from the regeneration end detection means and the output of the error amplifier. Those having a determining means.

Further, a series circuit composed of the first winding of the transformer, the main switch element and the input power source, a rectifying field effect transistor connected to the second winding of the transformer, and a freewheeling field effect. Type DC / DC converter including a transistor, an error amplifier for amplifying a difference between an output voltage of the conversion circuit and a voltage of a reference power supply, and a regeneration for detecting completion of regeneration of excitation energy of the transformer to an input power supply. The end detection means, the signal from the regeneration end detection means and the output of the error amplifier turn on / off the main switch element.
A means for determining off-timing is provided, and when the main switching element is non-conducting, the excitation energy of the transformer is supplied to the input power source by resonance between the excitation inductance of the transformer and the electrostatic capacity of the field effect transistor. It regenerates. Further, the drive signals of the rectifying field effect transistor and the free wheeling field effect transistor are obtained by the voltage induced in the transformer.

The means for detecting the end of regeneration of the excitation energy of the transformer to the input power supply includes the fourth winding of the transformer.

Further, the regeneration end detecting means includes a comparison circuit for comparing the voltage applied to the main switch element and the voltage of the input power supply.

The means for determining the off-timing of the main switch element is a comparison circuit for comparing the output of the error amplifier with the switching current signal flowing in the main switch element, or the regeneration end detecting means from the output of the error amplifier. A comparison circuit that compares the signal obtained by subtracting the output signal of the triangular wave oscillator or the sawtooth wave oscillator controlled by the output with the switching current signal of the main switch element, or the output signal of the triangular wave oscillator or the sawtooth wave oscillator to the switching current signal. Is one of the comparison circuits for comparing the signal obtained by adding and the output of the error amplifier.

The means for determining the off timing of the main switch element is a comparison circuit for comparing the output of the error amplifier with the current signal flowing in the output circuit of the converter, or the regeneration end detecting means of the output of the error amplifier. A comparator circuit that compares a signal obtained by subtracting the output signal of a triangular wave oscillator or a sawtooth oscillator controlled by the output with a current signal that flows in the output circuit, or adds the output signal of the triangular wave oscillator or the sawtooth oscillator to the current signal. Is one of the comparison circuits for comparing the output signal of the error amplifier with the output signal.

A field effect transistor is used instead of the rectifying diode and the free wheeling diode, and the drive signal of the field effect transistor is obtained by the voltage induced in the transformer.

[0016]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a block diagram showing a DC / DC converter according to a first embodiment of the present invention. In the figure, 1
Is an input power source, 10 is a rectifying diode, 11 is a free-wheeling diode, 12 is a smoothing reactor, 13 is a smoothing capacitor, 14 is a load, and 18 is a reference power source. , Or a corresponding portion, and detailed description thereof will be omitted.

Reference numeral 26 is a transformer, and 26a is the first thereof.
, A second winding 26b, and a third winding 26c. Reference numeral 27 is a field effect transistor as a main switching element connected to the first winding 26a of the transformer 26 and the input power supply 1, and 28 is a diode for resetting the transformer connected to the third winding 26c and the input power supply 1. . 29, 30
Is a resistor for dividing the output voltage, 31 is an error amplifier that amplifies the difference between the output voltage and the reference power supply 18, 32 is a triangular wave oscillation circuit, and 33 is a comparison circuit for the error amplifier 3
The output signal of 1 and the output signal of the triangular wave oscillation circuit 32 are compared. 34 is a drive circuit for driving the main switch element 27, 26d is a fourth winding for detecting the voltage induced in the transformer 26, 35 is a resistor connected to the fourth winding 26d, and 36 is a comparison. Circuit. 37 is a switching frequency varying means, which is a one-shot multivibrator 38 and a resistor 39 for determining the output pulse width thereof,
It is composed of a capacitor 40 and a field effect transistor 41 as a switch element. Reference numerals 42 and 43 respectively denote a timing capacitor and a timing resistor of the triangular wave oscillation circuit 32.

FIG. 2 is an operation waveform diagram of the DC / DC converter of FIG. It should be noted that FIG. 7A shows the waveform of the drain-source voltage V _DSO of the main switch element 27, FIG. 7B shows the waveform of the induced voltage V _DET of the transformer, and FIG.
Is a waveform at the output point A of the comparison circuit 36, FIG. 7 (d) is a waveform at the output point B of the one-shot multivibrator 38, and FIG. 7 (e) is an output point C of the error amplifier 31 and the output of the triangular wave oscillation circuit 32. The waveform at the point D, the waveform (f) in the figure is the waveform at the output point E from the comparison circuit 33.

Next, the operation will be described. As shown in FIG. 2E, when the output D of the triangular wave oscillation circuit 32 exceeds the output C of the error amplifier 31 which amplifies the difference between the output voltage and the reference power source 18 at time t ₁ , the output E of the comparison circuit 33 is changed. Figure 2 (f)
Becomes 0, and the drive circuit 34 becomes the main switch element 27.
To the main switch element 27 to turn off the main switch element 27.
When the main switching element 27 is turned off, the transformer resetting diode 28 is turned on, and the excitation energy stored in the transformer is regenerated from the third winding 26c to the input power supply 1 when the main switching element 27 is on. When the excitation energy is completely regenerated at time t ₂ , the drain-source voltage of the main switch element 27 drops to the input power supply voltage V _IN as shown in FIG. 2A, and the induced voltage V _{DET of the} transformer is also shown in FIG.
As shown in (b), since it decreases to 0, the output A of the comparison circuit 36 decreases. The one-shot, which constitutes the switching frequency varying means 37, is formed by the falling signal of the output A.
The multivibrator 38 outputs a pulse as shown in FIG. 2D, and turns on the switch element 41. As a result, the timing capacitor 42 of the triangular wave oscillator circuit 32 is short-circuited, and the oscillation cycle changes as shown in FIG. As a result, the switching frequency can be changed. The pulse width of the one-shot multivibrator 38 is the resistance 39,
The capacitor 40 is set to a value sufficient to discharge the electric charge of the timing capacitor 42 of the triangular wave oscillator circuit 32.

At time t ₂ , when the output C of the error amplifier 31 falls below the output D of the triangular wave oscillation circuit 32 as shown in FIG. 2 (e), the output E of the comparison circuit 33 becomes high as shown in FIG. 2 (f). Then, the drive circuit 34 gives an ON signal to the main switch element 27, and the main switch element 27 is turned ON. As a result, the voltage between the drain and source of the main switch element 27 is shown in FIG.
As shown in (a), it drops to 0 and the induced voltage V of the transformer
_DET also becomes negative as shown in Fig. 2 (b).

At time t ₃ , when the output C of the error amplifier 31 exceeds the output D of the triangular wave oscillation circuit 32 as shown in FIG. 2 (e), the output E of the comparison circuit 33 becomes 0 as shown in FIG. 2 (f). Then, the drive circuit 34 again gives an off signal to the main switch element 27, and the main switch element 27 is turned off. The above operation is repeated.

Since the rectifying / smoothing operation on the side of the second winding 26b of the transformer is the same as the conventional operation, its explanation is omitted.

As described above, according to the first embodiment,
Since the control of the on / off timing of the main switch element is configured not to consume the excitation energy of the transformer,
The excitation energy can be regenerated to the input power source, and there is the effect that a DC / DC converter with good power conversion efficiency can be obtained.

The means for detecting the end of regeneration of the excitation energy of the transformer to the input power source has been described in the above embodiment in which the transformer induced voltage detecting winding 26d is provided. 26a voltage and second winding 2
The end of regeneration of the excitation energy of the transformer to the input power source may be detected from the voltage of 6b.

Embodiment 2 In the first embodiment, the fourth winding is used as a means for detecting the end of regeneration of the excitation energy of the transformer to the input power supply. However, a comparison circuit that compares the voltage applied to the main switch element with the voltage applied to the input power supply. However, the same effect as that of the first embodiment can be obtained.

FIG. 3 is a block diagram showing a DC / DC converter according to a second embodiment of the present invention. In FIG.
1, 10-14, 18, 26-34, and 37-43
1 are the same as or equivalent to those of the first embodiment denoted by the same reference numerals in FIG. 1, and therefore detailed description will be omitted.

Reference numerals 44 and 45 denote resistors for detecting the voltage divided between the drain and source of the main switch element 27, and 46 and 4 respectively.
Reference numeral 7 is a resistor for detecting the voltage division of the input power supply 1. Reference numeral 48 is a comparison circuit for comparing the drain-source voltage of the main switch element 27 with the voltage of the input power supply 1.

Next, the operation will be described. The operation of determining the off-timing of the main switch element 27 and the rectifying / smoothing operation of the transformer on the side of the second winding 26b are the same as those in the first embodiment, and therefore their explanations are omitted. When the main switching element 27 is turned off, the transformer resetting diode 28 is turned on, and when the main switching element 27 is turned on, the excitation energy stored in the transformer is applied to the third winding 26c.
Is regenerated to the input power supply 1. When the excitation energy is completely regenerated, the drain-source voltage of the main switch element 27 drops to the input power supply voltage V _IN , and the output A of the comparison circuit 48 comparing the input voltage drops. The one-shot multivibrator 38, which constitutes the switching frequency varying means 37, outputs a pulse by the falling signal of the output A, as in the first embodiment, and the switching element 4
Turn on 1. As a result, the timing capacitor 42 of the triangular wave oscillator circuit 32 is short-circuited, and the oscillation cycle changes.
As a result, the switching frequency can be changed.

When the output D of the triangular wave oscillation circuit 32 becomes lower than the output C of the error amplifier 31, the output E of the comparison circuit 33 becomes high, the drive circuit 34 gives an ON signal to the main switch element 27, and the main switch element 27 becomes It turns on.

Embodiment 3 4 is a block diagram showing a DC / DC converter according to a third embodiment of the present invention. In FIG. 4, 1, 10, 14, 18, 26-30, 3,
Reference numerals 2 and 35 to 43 are the same as or equivalent to those in the first embodiment denoted by the same reference numerals in FIG. 1, and therefore detailed description thereof will be omitted.

Reference numeral 49 is an error amplifier for amplifying the difference between the output voltage and the reference voltage source 18, 50 is a switching current detecting means such as a resistor for detecting the current flowing through the main switching element 27, and 51 is an output C of the error amplifier. A comparison circuit for comparing the switching current detection value F, 52 is a triangular wave oscillation circuit 3
2 is a differential circuit for differentiating the output D, 53 is an inverter, 5
Reference numeral 4 is an RS flip-flop circuit, and 55 is a drive circuit that receives the output signal of the RS flip-flop circuit 54 and drives the main switching element 27.

FIG. 5 is an operation waveform diagram of the DC / DC converter of FIG. Incidentally, FIG. 7A shows the waveform of the drain-source voltage V _DSO of the main switch element 27, FIG. 7B shows the waveform of the output point B of the one-shot multivibrator 38, and FIG. Output D of circuit 32
Waveforms at points, (d) in the figure shows the RS flip-flop circuit 5
4 shows a set input signal waveform, FIG.
Waveforms of the output C and the switching current detection value F of FIG. 6, (f) of FIG. 6 shows the reset input signal waveform of the RS flip-flop circuit 54, and (g) of FIG. 6 shows the output signal waveform of the RS flip-flop circuit 54. This is the waveform of the output E of the drive circuit 55.

Next, the operation will be described. As shown in FIG. 5E, when the switching current detection value F detected by the switching current detection means 50 at time t ₁ matches the output C of the error amplifier 49, the output of the comparison circuit 51 is as shown in FIG. 5F. Then, the output is input to the reset input R of the RS flip-flop circuit 54, and the RS flip-flop circuit 54 is reset. As a result, the output Q of the RS flip-flop circuit 54 becomes 0 as shown in FIG. 5G, and the main switch element 27 receives the off signal E from the drive circuit 55 and turns off.

On the other hand, when the main switch element 27 is turned off at time t ₁ , the transformer resetting diode 28 is turned on, and the exciting energy of the transformer is supplied from the third winding 26c to the input power source 1 according to the first or second embodiment. It regenerates similarly.
When the excitation energy is completely regenerated at time t ₂ ,
As shown in (a), the drain-source voltage of the main switching element 27 drops to the input power supply voltage V _IN , and the induced voltage V _{DET of the} transformer also drops to 0. Therefore, the output A of the comparison circuit 36 is
Goes down. By the falling signal of the output A, the one-shot multivibrator 38 which constitutes the switching frequency varying means 37 outputs a pulse as shown in FIG. 5B, and the switch element 41 is turned on. As a result, the timing capacitor 42 of the triangular wave oscillator circuit 32 is short-circuited, and the oscillation cycle changes as shown in FIG. As a result, the switching frequency can be changed.

At time t ₂ , the output D of the triangular wave oscillator circuit 32
The end of one cycle is detected by the differentiating circuit 52, and this signal is inverted by the inverter 53, so that the RS flip-flop circuit 54 is given a set input S as shown in FIG. The -S flip-flop circuit 54 is set. As a result, the output Q of the RS flip-flop circuit 54 becomes high as shown in FIG. 5G, and the main switch element 27 receives the ON signal E from the drive circuit 55 and turns ON.

At time t ₃ , the switching current detection value F
However, when the output C of the error amplifier 49 and the output C of the error amplifier 49 again match as shown in FIG. 5E, the output of the comparison circuit 51 becomes high as shown in FIG. 5F and the reset input R of the RS flip-flop circuit 54 becomes high. The output is input and the RS flip-flop circuit 54 is reset. As a result, the output Q of the RS flip-flop circuit 54 becomes 0 as shown in FIG. 5G, and the main switch element 27 receives the off signal E from the drive circuit 55 again and turns off. The above operation is repeated.

Since the rectifying / smoothing operation on the side of the second winding 26b of the transformer is the same as the conventional operation, its description is omitted.

As described above, according to the third embodiment,
The excitation energy of the transformer can be regenerated to the input power source, and a DC / DC converter with good power conversion efficiency can be obtained, and a DC / DC converter with good control characteristics can be obtained.

Fourth Embodiment In the third embodiment,
The means for deciding the OFF timing of the main switch element was shown to be composed of a comparison circuit that compares the output of the error amplifier with the switching current signal flowing in the main switch element. It may be configured by a comparison circuit that compares the signal obtained by subtracting the output signal of the wave oscillator with the switching current signal that flows in the main switch element, and the effect of further improving the control stability as compared with the third embodiment. There is.

FIG. 6 is a block diagram showing a DC / DC converter according to a fourth embodiment of the present invention. In FIG. 6, those denoted by the same reference numerals as those in FIG. 4 are the same as or equivalent to those in the third embodiment, and therefore detailed description thereof will be omitted.

Reference numeral 56 is a subtractor for subtracting the output D of the triangular wave oscillator from the output C of the error amplifier. In the operation of this embodiment, the comparison circuit 51 detects the switching current detection value F,
The difference is that the output C of the error amplifier 49 is subtracted from the output of the triangular wave oscillator or the output signal D of the sawtooth wave signal from the triangular wave or sawtooth wave signal, and the subsequent operation is similar to that of the third embodiment. Therefore, detailed description will be omitted.

Embodiment 5 FIG. In the fourth embodiment,
The means for determining the off-timing of the main switch element is composed of a comparison circuit for comparing the signal obtained by subtracting the output signal of the triangular wave oscillator or the sawtooth wave oscillator from the output of the error amplifier with the switching current signal flowing in the main switch element. However, it may be configured by a comparison circuit that compares the output of the error amplifier and the signal obtained by adding the output signal of the triangular wave oscillator or the sawtooth wave oscillator to the switching current signal flowing in the main switch element, The same effect as that of the fourth embodiment is obtained.

FIG. 7 is a block diagram showing a DC / DC converter according to a fifth embodiment of the present invention. In FIG. 7, the components denoted by the same reference numerals as those in FIG. 6 are the same as or equivalent to those in the fourth embodiment, and therefore detailed description thereof will be omitted.

Reference numeral 57 is an adder for adding the output D of the triangular wave oscillator or the sawtooth wave oscillator to the switching current signal F flowing in the main switch element. The operation of this embodiment is different only in that the comparison circuit 51 compares the output C of the error amplifier 49 with the triangular wave or sawtooth wave signal obtained by adding the output D of the triangular wave oscillator or the sawtooth wave oscillator to the switching current signal. Since the subsequent operation is the same as that of the fourth embodiment, detailed description thereof will be omitted.

Embodiment 6 FIG. In addition, the third to fifth embodiments
In the above, the one using the switching current detection signal of the main switch element is shown, but the one using the current detection signal flowing in the rectifying diode on the second winding side of the transformer which becomes conductive when the main switch element is on. Alternatively, the exciting current is not superimposed on the current detection signal used in the third to fifth embodiments, so that the controllability is improved.

FIG. 8 is a block diagram showing a DC / DC converter according to a sixth embodiment of the present invention. In FIG. 8, those denoted by the same reference numerals as those in FIG. 4 are the same as or equivalent to those in the third embodiment, and detailed description thereof will be omitted.

Reference numeral 58 is a means for detecting the current flowing through the rectifying diode 10 on the side of the second winding 26b of the transformer. Since the operation of this embodiment is almost the same as that of the third embodiment, detailed description thereof will be omitted. Since the current detection signal F in the present embodiment does not include an exciting current component that is not directly related to energy transfer to the load,
It is not affected by the change in the gradient of the exciting current that changes due to the fluctuation of the input voltage.

As in the fourth or fifth embodiment, the output signal D of the oscillation circuit is subtracted from the output signal C of the error amplifier by using a subtractor, or the output signal D of the oscillation circuit is added. It may be configured to add to the current detection signal F flowing through the rectifying diode 10 by using a power supply device.

As described above, according to the sixth embodiment,
Since it is not affected by the change in the gradient of the exciting current that changes due to input voltage fluctuations, the DC characteristics are very good.
There is an effect that a DC converter is obtained.

Embodiment 7 FIG. In the sixth embodiment,
The one using the current detection signal flowing through the rectifying diode on the second winding side of the transformer, which becomes conductive when the main switch element is on, has been described, but it uses the current detection signal flowing through the smoothing reactor 12. It may be present, and the same effect as that of the sixth embodiment is obtained.

FIG. 9 is a block diagram showing a DC / DC converter according to a seventh embodiment of the present invention. In FIG. 9, the elements denoted by the same reference numerals as those in FIG. 8 are the same as or equivalent to those in the sixth embodiment, and therefore detailed description thereof will be omitted.

Reference numeral 59 is a means for detecting the current flowing through the smoothing reactor 12. Since the operation of this embodiment is almost the same as that of the sixth embodiment, detailed description thereof will be omitted. As in the sixth embodiment, the current detection signal in the present embodiment does not include the exciting current component that is not directly related to the energy transfer to the load, and therefore the gradient of the exciting current that changes due to the input voltage fluctuation. To be unaffected by changes in.

As in the fourth or fifth embodiment, the output signal D of the oscillation circuit is subtracted from the output signal C of the error amplifier by using a subtractor, or the output signal D of the oscillation circuit is added. It may be configured to add to the current detection signal F flowing through the smoothing reactor 12 by using a device.

Embodiment 8. In addition, the first to seventh embodiments
In the above, the rectifying diode and the free wheeling diode are used on the second winding side of the transformer, but a field effect transistor may be used, and the voltage drop value during conduction can be reduced. Therefore, there is a loss reduction effect.

FIG. 10 is a block diagram showing a DC / DC converter according to an eighth embodiment of the present invention. In FIG. 10, the components denoted by the same reference numerals as those in FIG. 1 are the same as or equivalent to those in the first embodiment, and thus detailed description thereof will be omitted.

Reference numeral 60 is a rectifying MOS field effect transistor (hereinafter abbreviated as rectifying MOSFET), and 61 is a freewheeling MOS field effect transistor (hereinafter, freewheeling M).
Abbreviated as OSFET. ), And the free-wheeling MOSFET 61
Of the second winding 26b of the transformer 26 is connected in the winding start direction (indicated by a circle), and the source terminal thereof is connected to the source terminal of the rectifying MOSFET 60. Also,
The drain terminal of the rectifying MOSFET 60 is the second winding 2
It is connected in the winding end direction of 6b. Rectifying MOSFE
The gate terminal of T60 is connected to the winding start direction of the second winding 26b, and the gate terminal of the freewheeling MOSFET 61 is connected to the winding end direction of the second winding 26b. The operations of the first winding 26a side and the control circuit of this embodiment are almost the same as those of the first embodiment, and therefore detailed description thereof is omitted.

FIG. 11 is an operation waveform diagram of the DC / DC converter of FIG. It should be noted that FIG.
Waveform of drain-source voltage V _DSO of Fig. 7, (b) of the same figure
Is the waveform of the voltage V ₂ of the second winding 26b of the transformer 26,
The figure (c) shows the waveform of the gate-source voltage V _GS1 of the rectifying MOSFET 60, and the figure (d) shows the freewheeling MOSFET.
61 is a waveform of the gate-source voltage V _GS2 of 61.

FIG. 12 is the third quadrant in the characteristic diagram of the MOSFET, where A is a sufficient gate voltage above the threshold voltage.
The characteristics when a source-to-source voltage is applied, B is the characteristics when the gate-source voltage is 0, that is, the characteristics of a diode parasitic on the MOSFET, and C is conventionally generally used as a rectifying or freewheeling diode. It is a characteristic of the Schottky barrier diode.

The operation of the second winding 26b side will be described below. In FIG. 11, when the main switch element 27 is turned off at time t ₁ , the voltage V ₂ of the second winding 26b becomes a negative voltage as shown in FIG. 11 (b). As a result, the gate-source voltage V _GS1 of the rectifying MOSFET 60 becomes 0 as shown in FIG.
No current flows through it. On the other hand, the freewheeling MOSFET 6
The gate-source voltage V _{GS2 of 1} is a positive voltage as shown in FIG. As shown in FIG. 12, when used in the third quadrant and given a sufficient gate-source voltage, the rectifying element has a lower voltage drop value when conducting than the Schottky barrier diode. This can reduce conduction loss. In a commonly used DC / DC converter of fixed switching frequency, the voltage V _{2 of} the second winding 26b becomes 0 when the reset of the magnetic flux of the transformer is completed,
Gate-source voltage V _{GS2 of the free-wheeling MOSFET 61}
Since it also becomes 0, there is a problem that there is a period in which the voltage drop value during conduction becomes higher than that of the Schottky barrier diode as shown in FIG. However, in the present embodiment, the main switching element is turned on at the same time when the magnetic flux of the transformer is reset, so that the current flows between the gate and the source of the freewheeling MOSFET 61 as shown in FIG. A sufficient voltage is always applied, and the MOSFET can be used as a rectifying element with a low voltage drop value.

When the main switching element 27 is turned on at time t ₂ , the voltage V of the second winding 26b is changed as shown in FIG. 11 (b).
₂ becomes a positive voltage. As a result, the rectifying MOSFET 6
The gate-source voltage V _GS1 of 0 acts as a rectifying element having a low voltage drop value, as a positive voltage is applied as shown in FIG. On the other hand, the gate-source voltage V _GS2 of the freewheeling MOSFET 61 becomes 0 as shown in FIG. 11D, and no current flows through the freewheeling MOSFET 61. The above operation is repeated.

As described above, according to the eighth embodiment,
Since the voltage drop value can be reduced and a sufficient drive voltage can always be applied while the field effect transistor is operating as a rectifying element, the field effect transistor functions as a synchronous rectifier to the maximum extent. As a result, the conduction loss can be greatly reduced, and there is an effect that a DC / DC converter with good power conversion efficiency can be obtained.

Ninth Embodiment In the eighth embodiment,
The one in which the rectifying MOSFET and the freewheeling MOSFET are driven by the voltage of the second winding of the transformer has been shown, but the winding for driving the rectifying MOSFET in the transformer and the freewheeling M
A separate winding for driving the OSFET may be provided, and since the drive voltage can be adjusted by the winding ratio, the drive voltage can be set considerably freely as compared with the ninth embodiment.

FIG. 13 is a block diagram showing a DC / DC converter according to a ninth embodiment of the present invention. In FIG. 13, those denoted by the same reference numerals as those in FIG. 11 are the same as or equivalent to those in the eighth embodiment, and detailed description thereof will be omitted.

26e is a rectifying MO wound around the transformer 26
The drive winding of the SFET 62, and the winding start direction (・
(Indicated by a mark) is connected to the gate terminal of the rectifying MOSFET 62, and the winding end direction is connected to the winding start direction of the second winding 26b. Further, 26f is a drive winding of the circulation MOSFET 62 wound around the transformer 26, and the winding start direction (indicated by a mark) of the winding is connected to the winding end direction of the second winding 26b, and the winding end direction is set. It is connected to the gate terminal of the free-wheeling MOSFET 61.

The drain terminal of the freewheeling MOSFET 61 is connected to the drain terminal of the rectifying MOSFET 62, and the source terminal is connected in the winding end direction of the second winding 26b. The source terminal of the rectifying MOSFET 62 is connected in the winding start direction of the second winding 26b of the transformer 26.

FIG. 14 is an operation waveform diagram of the DC / DC converter of FIG. It should be noted that FIG.
Waveform of drain-source voltage V _DSO of Fig. 7, (b) of the same figure
Is the waveform of the voltage V ₂ of the second winding 26b of the transformer 26,
FIG. 6C shows the waveform of the gate-source voltage V _GS1 of the rectifying MOSFET 62, and FIG.
61 is a waveform of the gate-source voltage V _GS2 of 61.

The operation of the ninth embodiment is that the drive voltage can be optimally adjusted by the number of turns of the drive winding, and FIG.
The operations are the same as those in the eighth embodiment except that the driving voltage at the time of OFF is negative as in (c) and (d), and thus detailed description of the operations is omitted.

Embodiment 10 FIG. In the eighth or ninth embodiment, the case where the excitation energy of the transformer is regenerated to the input power source by using the third winding of the transformer and the transformer resetting diode has been described.
May be used to regenerate the exciting energy of the transformer to the input power source by resonance of the exciting inductance of the transformer and the electrostatic capacity of the MOSFET without using the winding of the transformer and the diode for resetting the transformer. Has the effect of reducing the size.

FIG. 15 is a block diagram showing a DC / DC converter according to a tenth embodiment of the present invention. In FIG. 15, the components denoted by the same reference numerals as those in FIG. 10 are the same as or equivalent to those in the eighth embodiment, and therefore detailed description will be omitted.

FIG. 16 is an operation waveform diagram of the DC / DC converter of FIG. It should be noted that FIG. 7A shows the waveform of the drain-source voltage V _DSO of the main switch element 27, FIG. 7B shows the waveform of the induced voltage V _DET of the transformer, and FIG.
Is a waveform at the output point A of the comparison circuit 36, (d) is a waveform at the output point B (omitted in FIG. 15) of the one-shot multivibrator in the oscillation frequency varying circuit 37, and (e) is an error amplifier. The waveform at the output C point of 31 and the output D point of the triangular wave oscillating circuit 32, the waveform (f) at the output E point of the comparison circuit 33, and the waveform (g) at the gate-source voltage VGS _{1 of the} rectifying MOSFET 60. Waveform, Figure (h) is the circulation MOSFE
It is a waveform of the gate-source voltage V _GS2 of T61.

Next, the operation will be described. When the output C of the error amplifier 31 exceeds the output D of the triangular wave oscillation circuit 32 at time t ₁ as shown in FIG. 16 (e), the output E of the comparison circuit 33 is output.
Becomes 0 as shown in FIG. 16F, the drive circuit 34 gives an OFF signal to the main switching element 27, and the main switching element 27
Turns off. When the main switching element 27 is turned off, the excitation energy stored in the transformer when the main switching element 27 is turned on causes the excitation inductance of the transformer 26, the drain-source capacitance of the rectifying MOSFET 60, and the gate-source capacitance of the freewheeling MOSFET 61. , And the resonance phenomenon with the electrostatic capacitance of the sum of the drain-source capacitance of the main switch element 27, the excitation energy of the transformer 26 is regenerated to the input power supply 1. At this time, rectifying MOSF
Drain-source capacitance of ET60 and freewheeling MOSFE
The gate-source capacitance of T61 acts on the primary side conversion value of the transformer 26. When the excitation energy is completely regenerated at time t ₂ , the drain-source voltage of the main switch element 27 drops to the input power supply voltage V _IN as shown in FIG. 16A, and the induced voltage V _{DET of the} transformer is also shown in FIG. 16B. ), The output A of the comparison circuit 36 decreases. By the falling signal of the output A, the one-shot multivibrator 38 which constitutes the switching frequency varying means 37 outputs a pulse as shown in FIG. 16 (d), and the switch element 41 is turned on. As a result, the timing capacitor 42 of the triangular wave oscillator 32 is short-circuited, and the oscillation cycle changes as shown in FIG. As a result, the switching frequency can be changed.

At time t ₂ , the output D of the triangular wave oscillation circuit 32
16E falls below the output C of the error amplifier 31 as shown in FIG. 16E, the output E of the comparison circuit 33 becomes high as shown in FIG. 16F, and the drive circuit 34 gives an ON signal to the main switch element 27. , The main switch element 27 is turned on. As a result, the drain-source voltage of the main switch element 27 drops to 0 as shown in FIG. 16A, and the induced voltage V _{DET of the} transformer also becomes negative as shown in FIG. 16B.

At time t ₃ , when the output C of the error amplifier 31 exceeds the output D of the triangular wave oscillation circuit 32 as shown in FIG. 16 (e), the output E of the comparison circuit 33 becomes 0 as shown in FIG. 16 (f).
Then, the drive circuit 34 again gives an off signal to the main switch element 27, and the main switch element 27 is turned off.

The operation of the transformer 26 on the side of the secondary winding 26b is performed in the off period t _{1 to} t _{2 of the} main switching element 27.
The gate-source voltage V _GS1 of the rectifying MOSFET 60 is 0 as shown in FIG.
No current flows through the ET60. On the other hand, the circulation MOS
The gate-source voltage V _GS2 of the FET 61 is shown in FIG.
It becomes positive as shown in (h), and it functions as a rectifying element having a low voltage drop value as shown in FIG.

ON period t ₂ of the main switching element 27
The t _3, the gate-source voltage V _GS1 of the rectifier MOSFET60 becomes a positive voltage as shown in FIG. 16 (g), it acts as a low rectifying element having a voltage drop value as shown in FIG. 12. On the other hand, the gate-source voltage V _GS2 of the _{freewheeling MOSFET 61} is 0 as shown in FIG.
No current flows in the SFET 61. Hereinafter, the above operation is repeated.

As described above, according to the tenth embodiment, the excitation energy of the transformer can be regenerated to the input power source by the resonance phenomenon, and the field effect transistor can function as a synchronous rectifier to the maximum extent so that the conduction loss can be greatly reduced. Since this can be reduced, there is an effect that the DC / DC converter with good power conversion efficiency can be downsized.

In the tenth embodiment, the second winding 2
6b voltage rectification MOSFET and freewheeling MOSFET
However, the transformer may be provided with a winding for driving the rectifying MOSFET and a winding for driving the freewheeling MOSFET separately as in the ninth embodiment.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a DC / DC converter according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a configuration diagram showing a DC / DC converter according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a DC / DC converter according to a third embodiment of the present invention.

FIG. 5 is a waveform diagram for explaining the operation of the third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a DC / DC converter according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a DC / DC converter according to a fifth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a DC / DC converter according to a sixth embodiment of the present invention.

FIG. 9 is a configuration diagram showing a DC / DC converter according to a seventh embodiment of the present invention.

FIG. 10 is a configuration diagram showing a DC / DC converter according to an eighth embodiment of the present invention.

FIG. 11 is a waveform diagram for explaining the operation of the eighth embodiment of the present invention.

FIG. 12 is a characteristic diagram for explaining characteristics of the field effect transistor used in the eighth embodiment of the present invention.

FIG. 13 is a configuration diagram showing a DC / DC converter according to Embodiment 9 of the present invention.

FIG. 14 is a waveform diagram for explaining the operation of the ninth embodiment of the present invention.

FIG. 15 is a configuration diagram showing a DC / DC converter according to a tenth embodiment of the present invention.

FIG. 16 is a waveform diagram for explaining the operation of the tenth embodiment of the present invention.

FIG. 17 is a configuration diagram showing a conventional DC / DC converter.

FIG. 18 is a waveform diagram for explaining the operation of the conventional example.

[Explanation of symbols]

1 input power source, 10 rectifying diode, 11 freewheeling diode, 12 smoothing reactor, 13 capacitor, 14 load, 18 reference power source, 26 transformer, 2
6a 1st winding, 26b 2nd winding, 26c 3rd
Winding, 26d fourth winding, 26e, 26f drive winding, 27 main switching element, 28 transformer resetting diode, 31, 49 error amplifier, 32 triangular wave oscillation circuit, 33, 36, 48, 51 comparison circuit, 34, 5
5 driving circuits, 37 switching frequency changing means, 3
8 one-shot multivibrator, 41 field effect transistor, 42 timing capacitor, 43
Timing resistor, 50, 58, 59 Current detector, 5
2 differentiating circuit, 53 inverter, 54 RS flip-flop circuit, 56 subtractor, 57 adder, 60,
62 rectifying MOSFET, 61 freewheeling MOSFET

Claims (8)

[Claims] 1. A series circuit composed of a first winding of a transformer, a main switching element, and an input power supply, which is connected in parallel to the first winding and the main switching element and which excites the transformer. A series circuit composed of a third winding of the transformer and a diode so as to regenerate energy to the input power source, a direct current having a rectifying diode and a circulating diode connected to the second winding of the transformer. A DC converter, an error amplifier for amplifying the difference between the output voltage of the conversion circuit and the voltage of the reference power supply, a regeneration end detecting means for detecting the end of regeneration of the excitation energy of the transformer to the input power supply, and the end of regeneration. DC / DC conversion comprising means for determining the on / off timing of the main switch element based on the signal from the detection means and the output of the error amplifier. apparatus. 2. A series circuit composed of a first winding of a transformer, a main switch element, and an input power supply, a rectifying field-effect transistor connected to the second winding of the transformer, and a free-field electric field effect. Type DC / DC converter including a transistor, an error amplifier for amplifying a difference between an output voltage of the conversion circuit and a voltage of a reference power supply, and a regeneration for detecting completion of regeneration of excitation energy of the transformer to an input power supply. An end detecting means, a means for determining the on / off timing of the main switch element by the signal from the regenerative end detecting means and the output of the error amplifier, and excites the transformer when the main switch element is not conducting. The excitation energy of the transformer is regenerated to the input power source by the resonance between the inductance and the electrostatic capacity of the field effect transistor. DC / DC converter characterized by 3. The DC / DC converter according to claim 2, wherein the drive signals for the rectifying field-effect transistor and the free-wheeling field-effect transistor are obtained by the voltage induced in the transformer.
DC converter. 4. The DC / DC converter according to claim 1, wherein the means for detecting the end of regeneration of the excitation energy of the transformer to the input power supply includes a fourth winding of the transformer. DC converter. 5. The DC / DC converter according to claim 1, wherein the regeneration end detecting means includes a comparison circuit for comparing the voltage applied to the main switch element and the voltage of the input power supply. DC converter. 6. The means for determining the off-timing of the main switch element is a comparison circuit for comparing the output of the error amplifier with the switching current signal flowing through the main switch element, or the regeneration end detecting means of the output of the error amplifier. A comparison circuit that compares the signal obtained by subtracting the output signal of the triangular wave oscillator or the sawtooth wave oscillator controlled by the output with the switching current signal of the main switch element, or the output signal of the triangular wave oscillator or the sawtooth wave oscillator to the switching current signal. The DC / DC converter according to any one of claims 1 to 5, wherein the DC / DC converter is any one of a comparison circuit for comparing a signal obtained by adding the signal and an output of the error amplifier. 7. The means for determining the off-timing of the main switch element is a comparison circuit for comparing the output of the error amplifier with the current signal flowing in the output circuit of the converter, or the regeneration end detection means of the output of the error amplifier. A comparator circuit that compares a signal obtained by subtracting the output signal of a triangular wave oscillator or a sawtooth oscillator controlled by the output with a current signal that flows in the output circuit, or adds the output signal of the triangular wave oscillator or the sawtooth oscillator to the current signal. 6. The DC / DC converter according to claim 1, wherein the DC / DC converter is any one of a comparison circuit that compares the output signal of the error amplifier with the output signal of the error amplifier. 8. A field effect transistor is used in place of the rectifying diode and the free wheeling diode, and a drive signal for the field effect transistor is obtained by a voltage induced in a transformer. Items 1, 4
7. The DC / DC converter according to any one of items 1 to 7.